I keep learning more on this subject. Cotton and flax are vegetable fibers. They don't have the spring that animal fibers have. If you don't knit tightly, there is a chance these yarns will drag down with the weight of the sweater and pull out of shape. Washing restores the shape, but there you are -- with a sagging sweater while you are wearing it. (Remember white cotton socks that always ran down at the heel because there was no elastic in the cuffs? That's the idea.) Here's what Claire Crompton says about cotton in The Knitter's Bible (David & Charles, c2006): "Cotton is a heavy yarn, so the weight of a finished garment can cause it to drop and the garment to get longer. It also lacks elasticity and so ribs become baggy, though this is restored after washing. Cotton blended with a synthetic fibre will have more stability. However cotton is a great yarn to use for crisp stitch textures and looks beautiful in lace knitting. Mercerized cotton has been treated to add lustre and take brighter dyes; it is stronger than untreated cotton and harder wearing."
There are some ways to get around this problem.
1. Choose light, open patterns that won't add to the weight of the sweater. (My Aran sweater is probably a poor pattern choice.)
2. You can knit cuffs with much smaller needles than suggested by the pattern. If the pattern says 8, use 6, for example.
3. You can also knit a thread of elastic into cuffs and wastebands. There are some small ones that can be in-obtrusive.
4. The best answer is to look for a yarn that is blended with a fiber that does have spring in it. 80% cotton, 20% wool; Cotton--synthetic; Cotton-silk.
As I plan this sweater for my friend, I thought I'd found the perfect yarn for Texas -- cotton/flax. Now that I've ordered it, I realize flax is going to have the same trouble as cotton. It's a plant product. I may be looking for that in-obtrusive elastic yet. Of course, the yarn is on back-order until the middle of May. I may never get it. The issue may resolve itself.
